Molded articles of methacrylic resin represented by polymethyl methacrylate not only exhibit excellent transparency and weather resistance, but also have beautiful appearance. Therefore, methacrylic resin molded articles are used as, for example, signboard parts, display parts, illumination parts, interior parts, structural parts, transport machine-related parts, electronic equipment parts, medical-related parts, optical-related parts, traffic-related parts, and the like. However, methacrylic resins have low impact resistance, and this defect limits an even wider application of methacrylic resins.
Various methods have been proposed to improve the impact resistance of methacrylic resins. For example, Patent Document 1 discloses a method of blending a multi-layered acrylic rubber produced by emulsion polymerization, into a methacrylic resin. This method is most widely used industrially at present. This multi-layered acrylic rubber comprises three or more layers, and has a spherical structure of substantially alternating layers of a rigid layer composed mainly of methyl methacrylate and a soft layer composed mainly of acrylic acid ester such as n-butyl acrylate. However, this method does not sufficiently improve the impact resistance of methacrylic resins. Additionally, while the multi-layered acrylic rubbers are blended into the methacrylic resin, the multi-layered acrylic rubbers may be condensed into lumps (gel colonies). Due to the lumps, hard spots (fish eyes) are generated in molded articles, and therefore their appearance is impaired.
Patent Document 1: Japanese Patent Examined No. 59-36645
Patent Document 2 discloses a method of polymerizing a monomer composed mainly of methyl methacrylate in the presence of a rubber-like material composed of a butadiene-butyl acrylate copolymer. However, this method still has problems such as poor appearance of molded articles resulted from poor dispersion of the rubber-like material.
Patent Document 2: Japanese Patent Examined No. 45-26111
Patent Document 3 discloses a method of polymerizing a monomer composed mainly of methyl methacrylate in the presence of a partially hydrogenated conjugated diene polymer. However, due to insolubility in methyl methacrylate, the partially hydrogenated conjugated diene polymer used in this method must be dissolved in other solvent, which complicates the production process. Further, granulation by phase inversion, particularly control of particle size, may be difficult in this method.
Patent Document 3: International Publication No. WO 96/032440
Patent Document 4 discloses a method using a modified block copolymer in place of the partially hydrogenated conjugated diene polymer used in Patent Document 3. The modified block copolymer used in this method comprises a (meth)acrylic acid alkyl ester unit and an aromatic vinyl monomer unit. According to the method of Patent Document 4, the control of particle size by phase inversion was easily achieved; however, the impact resistance of obtained molded articles was not sufficient.
Patent Document 4: Japanese Patent Laid-Open No. 2000-313786
Patent Document 5 discloses a polymer composition comprising a component (a): 1 to 50 parts by mass of an acrylic acid ester polymer or a methacrylic acid ester polymer, and a component (b): 50 to 99 parts by mass of an epoxy-modified block polymer obtained by epoxidizing an unsaturated carbon double bond of a conjugated diene compound in a block copolymer composed of a polymer block A composed mainly of a vinyl aromatic compound and a polymer block B composed mainly of the conjugated diene compound in one molecule. According to the polymer composition of Patent Document 5, the compatibility of methacrylic resin and rubber polymer is improved; however, the impact resistance is not sufficient.
Patent Document 5: Japanese Patent Laid-Open No. 7-207110
Patent Document 6 discloses a methacrylic resin composition obtained by template polymerization, the composition comprising: 50 to 99% by mass of polymethyl methacrylate or a copolymer composed mainly of methyl methacrylate; 0 to 50% by mass of an ethylene-vinyl acetate copolymer; and 0.5 to 50% by mass of a graft copolymer containing polymethyl methacrylate or a copolymer composed mainly of methyl methacrylate and polyvinyl acetate and/or ethylene-vinyl acetate copolymer, and/or a block copolymer containing polymethyl methacrylate or a copolymer composed mainly of methyl methacrylate and polyvinyl acetate or ethylene-vinyl acetate copolymer. However, the methacrylic resin composition of Patent Document 6 has low transparency, and the impact resistance is still not sufficient.
Patent Document 6: Japanese Patent Laid-Open No. 6-345933
Patent Document 7 discloses a method of producing a methacrylic resin molding material with excellent impact resistance and processability, the method comprising reacting methyl methacrylate with a block copolymer composed of a conjugated diene polymer component rich in vinyl bonds and an acrylic acid ester or methacrylic acid ester polymer component, under the polymerization conditions. However, when the molding material obtained by this method was kneaded using a Labo Plastmill, etc., for molding, the morphology was broken and the impact resistance was reduced.
Patent Document 7: Japanese Patent Laid-Open No. 49-45148